A power transmission mechanism is conventionally know which includes a drive source and two planetary gear mechanisms. For example, a driving force distribution system 1 described in Patent Literature 1 includes, as show in FIG. 21, two planetary gear mechanisms PL each including a ring gear R, planetary gears P, a planetary carrier C and a sun dear S and two power sources having a drive motor 102 that gives a driving force to a shaft 101 that connects together the sun gears S of the two planetary gear mechanisms PL and a control motor 103 that generates a difference in driving force between left and right wheels. Then, according to the description of Patent Literature 1, the driving force distribution system 100 can be controlled so that a driving force sum of the left and right wheels that influences a front-rear motion (behavior) of a wheeled vehicle is given by driving the drive motor 102 while by driving the control motor 103 as required while running by means of the driving force of the drive motor 102 , a driving force difference of the left and right wheels that influences a turning motion (behavior) of the wheeled vehicle is given.
Namely, the driving force distribution system 100 described in Patent Literature 1 includes the two power sources (the drive motor 102, the control motor 103) and can control simultaneously both the driving force sum of the left and right wheels that influences mainly the front-rear motion (behavior) of the wheeled vehicle and the driving force difference of the left and right wheels that influences mainly the turning motion (behavior) of the wheeled vehicle.
Additionally Patent Literature 2 discloses a left and right wheel coupling unit in which a transmission system including two gears is provided at one side of a bevel differential gear that is connected to a motor and a transmission system including two gears and a transmission system including three gears are provided via a switching device at the other side of bevel differential gear. In the transmission system including the two gears that is provided at the other side of the bevel differential gear, a gear ratio thereof is set to be the same as that of the transmission system including the two gears that is provided at the one side of the bevel differential gear. In the transmission system including the three gears that is provided at the other side of the bevel differential gear, a gear ratio thereof is set to be the same as that of the transmission system including the two gears that is provided at the one side of the bevel differential gear, these two gear rations being opposite to each other in working direction and equal to each other in absolute value. According to this coupling unit, when the transmission system including the two gears is selected by the switching device, the torque of the motor is transmitted to the left and right wheels in the same direction and in the same magnitude, whereby a forward start or a reverse start can be assisted. When the transmission system including the three gears is selected, the torque of the motor is transmitted to the left and right wheels in the opposite directions and in the same magnitude, whereby a turning assist can be provided in which a yaw moment is generated in a turning direction.